An ultrasound inspection apparatus irradiates a subject (hereinafter, referred to as a “work” in some cases) as an inspection object with an ultrasound wave, receives a reflected or transmitted ultrasound wave using an ultrasound probe (hereinafter, referred to as a “probe” in some cases) , and forms an image. For example, in a case where the work is an electronic device, there is a need to detect a minute defect, and thus the ultrasound inspection apparatus needs to have high resolution. When the ultrasound inspection apparatus uses a high-frequency ultrasound wave, high resolution is achieved; on the other hand, there is a concern that attenuation of the ultrasound wave will be increased and thus, an S/N ratio will be lowered. Since the ultrasound wave is attenuated in water less than in air, normally, the work is immersed in water and ultrasound inspection is often performed, with water filled between the tip of the probe and a surface of the work. The ultrasound inspection apparatus focuses on an interface in the work as an observation target, scans the probe, and forms an image of the obtained result, while a distance (hereinafter, referred to as a “water distance” in some cases) between the tip of the probe and the surface of the work is maintained to be a predetermined value,. In this manner, a position, a shape, and a depth of the defect can be found.
Wetting the electronic device in water results in failure such as corrosion or metallic contamination. Therefore, in the related art, sampling inspection has been performed for ultrasound inspection of the electronic device. However, only one defect in an in-vehicle electronic device or the like results in a significant loss in some cases. There is a growing need for 100% inspection such that even one defect does not occur after shipment. In other words, in the inspection of such an important component, there is a need to avoid wetting as much as possible and to perform the inspection at a high speed.
The ultrasound probe is broadly divided into a single probe in which one ultrasonic vibration element is disposed, and an array probed in which multiple ultrasonic vibration elements are arranged in a row. The single probe performs transmission and reception of the ultrasound wave using the single ultrasonic vibration element. The array probe transmits and receives one ultrasonic pulse beam with a plurality of groups of ultrasonic vibration elements arranged in a row, in which the group is formed of a few ultrasonic vibration elements which are connected to each other.
The ultrasound inspection apparatus including the array probe transmits a wave transmitting signal (excitation signal) to each of the ultrasonic vibration elements constituting the plurality of groups of ultrasonic vibration elements. The ultrasound inspection apparatus further receives a wave receiving signal (echo wave receiving signal) from each of the ultrasonic vibrators. The ultrasound inspection apparatus applies a predetermined time lag (delay pattern) to the wave transmitting signal (excitation signal) and the wave receiving signal (echo wave receiving signal), and causes the elements to function as a so-called phased array. In this manner, the ultrasound inspection apparatus can concentrate an ultrasonic beam to a focus and can obtain an ultrasonic echo having a focal point. Curvature is applied in a direction orthogonal to an arrangement direction of the ultrasonic vibration elements, thereby making it possible to concentrate the ultrasonic beam to the focus also in the direction orthogonal to the arrangement direction such that the ultrasonic echo having a focal point is obtained. In the array probe, the plurality of groups of ultrasonic vibrators that transmits the ultrasonic pulse beams are electronically scanned, thereby making it possible to perform measurement at a high speed. In a case of inspecting a large work such as an insulated gate bipolar transistor (IGBT) or a silicon wafer, the array probe is used to increase throughput in some cases.
In a case of inspecting a work such as an electronic device that is vulnerable to water, as shown in FIG. 1 in PTL 1, there is proposed a type of local-immersion probe, which is disposed below a work having an inspection surface facing downward and suctions up water around the probe. On page 8 in PTL 1, the following description is provided. “As shown in FIG. 1, acoustic coupling of the ultrasonic beam to the wafer is enhanced by a column of water or other fluid 110 that is maintained by flowing fluid from one or more positions in close proximity to the transducer.”